This invention relates to a sod harvesting device, comprising a mobile chassis with a first knife that is capable of cutting a sod free from a field, and a second knife that is capable of chopping the sod in a direction that is transverse to the direction of travel, whereby the second knife is equipped with electronically controlled mechanisms that allow the second knife to work into the sod when a desired sod length has been reached, and where transport mechanisms are present near to the first knife to collect the cut away sod and to carry it away.
Such a device is mainly used for the harvesting of cultivated turfs. A known device for the harvesting of grass turfs contains a chassis that is possibly self-propelled and contains a first knife on the front side, when viewed in the direction of travel, for cutting away a sod of a certain width and thickness from the field. The knife thus grasps at the desired thickness below ground level, while a drum rolls over the field next to the knife in order to enclose the sod between the knife and the drum so that a uniform thickness is obtained. Moreover, the device contains a second knife that is activated after the desired length of grass turf has been cut away, in order to chop the sod transverse to the longitudinal direction. The sod that has been harvested to the desired length is guided behind the first knife to a means of transport in the form of a conveyor belt that carries it away. In the meantime, the next grass turf is already cut away.
The known device operates automatically to a certain extent since the second knife rests under considerable spring tension on a cam disc and is always released when this cam disc turns, where the cam disc is linked to the drum via a chain drive. After an exact predetermined number of revolutions of the drum, the second knife is activated and the harvested sod is chopped. A drawback of this is that the transition to a different sod length requires relatively major adjustment of the device since in order to achieve this, a different gear ratio must be obtained in the chain drive. In practice, this means that the existing gear wheels must be removed in order to make room for other gear wheels. This not only takes time and results in the device being out of service, but is above all relatively inaccurate since only lengths that match a specific gear ratio can be used. In practice, it is often desirable to adjust the length of the grass turf rather accurately in order to ensure that the diameter of a roll of turf is virtually constant. If, during the harvesting, due to the subsoil, a different depth is used for the first knife, this means that a different length must also be chosen in order to obtain the same diameter. This cannot, or is almost impossible to achieve using the known device.
Moreover, the known device is rather inaccurate since the drum often slips due to the resistance that the drum encounters in the chain drive and the limited friction on the field. This results in the harvested sod having a greater length than was intended. This is in any event what happens to the sod that is first to be harvested after the device starts operating. The distance between the drum and the second knife will inevitably cause this sod harvested over this distance to be too long, with this having to be manually corrected and resulting in rejection of the relevant sod part.
A somewhat better construction is revealed by the sod harvesting apparatus disclosed in U.S. Pat. No. 4,966,239. Also this apparatus comprises a harvesting knife in the front section of the machine capable of cutting loose a sod from the field together with a cutting knife which is capable of cutting the sod in the traverse direction over it""s entire thickness once the desired length is obtained. Different from the prior art device described hereinbefore, the apparatus known from this US patent comprises electronic means for determining the length of sod and an electronic signal is given to the cutting knife in order to cut the sod . These electronic means consist of a inductive, eddy current pick up which counts the number of passing teeth on a gear in the harvesting transmission and sends pulses to an electronic pre-determining counter. The counter sends a signal to actuation means of the cutting life once a programmed number of pulses is exceeded, which causes the sod being cut. Although this allows for more precise, finer and especially much more easily finer setting of the desired length compared to the previously described prior art device, also this device does not take into account any irregularities which may arise in the harvested product, such as interruptions and temporary variations in the length of the product due to stretching and crimping. In stead just the number of revolutions of the gear wheel is taken as a basis for activating the cutting knife.
This invention is intended, in a device of the type mentioned in the introduction, to ensure that these disadvantages are barely apparent, and in particular, to ensure that a fine adjustment is available for the harvested sod length.
In order to attain this objective, according to the invention, a device of the type mentioned in the introduction, is characterised in that an electronic sensor installed near to a conveyor track for the sod is at least capable of recording a size for a length of passing sod and producing this as an electronic signal, and that the sensor is linked by electronic means to the electronically controlled mechanisms for the second knife in order to release the second knife upon reaching a predetermined sod length. Thus the invention provides a sensor that directly or indirectly measures the length of the passing sod, unlike the known device where the rotation of the drum essentially represents a displacement of the device as a whole. Thus, in the device according to the invention, the sod that is first to be harvested will be processed in the same way as successive sod s. Since measuring takes place after the harvesting, instead of before as is the case for the known device, the device according to the invention is thus much less susceptible to stretching and shrinking of the harvested sod s that can result from a difference in speed between the discharge rates of the transport mechanisms and the driving speed of the device as a whole. In accordance with the invention, the length of the grass turf can be recorded as the grass turf is ultimately delivered. Since the invention is based on an electronic sensor and the same transmission to the second knife, measuring can take place virtually without any friction, and the sod can be adjusted electronically to any desired length, without having to take the device out of service to do this.
A preferred embodiment of the device according to the invention is characterised in that the sensor is linked to the electronically controlled mechanisms via the medium of a central processing unit. The central processing unit enables other relevant parameters to be taken into account, such as the actual thickness of the sod, so that an optimal end product can be obtained.
In a particular embodiment, the device according to the invention is characterised in that the electronic sensor contains a measuring wheel to rest on a passing sod and to be driven by it, and that a sensor is linked to the measuring wheel that records a rotation of the measuring wheel and produces an electronic signal. In this case, the harvested sod is directly measured in order to obtain an extremely accurate measuring result. This measuring result is sent to the central processing unit for further processing.
A preferred embodiment of the device is characterised in that the sensor is capable of recording the direction of rotation of the measuring wheel. Since the sensor is capable of not only sensing a rotation, but also the direction of rotation of the measuring wheel, the travelling forwards and backwards and any shocks in the transportation of the sod can be taken into account, so that the final length of the sod is not altered. A particular embodiment, the device according to the invention is, in this respect, characterised in that the sensor contains an incremental pulse generator.
Another preferred embodiment of the device according to the invention is characterised in that an electronic means of detection is used to record the presence of a sod in the conveyor track and to produce this as an electronic signal. This results in not only the length of the harvested sod being measured, but the presence of the sod in the conveyor track also being detected, and this is produced as an electronic signal. In particular, the length of the harvested sod is determined, indirectly, if not on the sod itself, thus allowing corrections to be made for the cases or periods when a sod is not in the conveyor track. This is in particular relevant for a length correction for the first sod to be harvested, and for a correction for gaps between consecutive sod s resulting from the occurrence of stretching and shrinking as previously described.
In a particular embodiment, the device according to the invention is characterised in the aforementioned context in that the sensor is essentially commonly suspended in a direction transverse to the conveyor track for the sod in order to be raised from a point of departure when a sod passes, and in that the means of detection is linked to a suspension attached to a sensor. This embodiment enables the presence or non-presence of a sod to be recorded in a relatively simple yet not less efficient manner. As soon as the sod is no longer present, the suspension will return to the point of departure and touch the means of detection that produces this as an electronic signal. In another embodiment, the device according to the invention is characterised in that the means of detection contains an electric switch that is capable of working together with the suspension attached to the sensor, at least when leaving its point of departure.
Because sod s are often rolled up after they have been harvested, with this roll preferably having a constant diameter, not only the length of the sod is important, but the thickness of the sod also plays a role. With this in mind, another embodiment of the device according to the invention is characterised in that means are installed next to a conveyor track for the sod in order to determine the thickness of a harvested sod and to produce this as an electronic value.
Another embodiment of the device according to the invention is characterised in that the sensor is commonly suspended in a direction transverse to the conveyor track and in that the means for determining the thickness of the sod contains a raise detector that is capable of recording an amount of raising of the sensor and producing this as an electronic value. The amount of raising provides a guideline for the actual thickness of the sod and can, as such, produce an electronic value, for example to a central processing unit Thus thickness variations in the sod s can be taken into account completely automatically, so that a constant diameter is attained when a sod is rolled up. Another particular embodiment of the device according to the invention is characterised in that the raise detector contains a slide resistor that is linked to the sensor. The raising of the measuring wheel thus results in a corresponding sliding in or sliding out of the slide resistor and the associated change in resistance that can be processed electronically.
Another embodiment of the device according to the invention is characterised in that the first knife is adjustable and is equipped with a means of adjustment that can be controlled by a central processing unit. Thus not only the length of the sod is controlled, but electronic control of the thickness is also possible with an electronic link between both in order to ensure that the final diameter of the rolled up product is constant. Thus, an extremely user-friendly system is obtained where, in practice, only one operator is required.
The means of adjustment can be implemented in several ways, for example, via the medium of a hydraulically or pneumatically controlled pressure cylinder. An embodiment of the device according to the invention that has been proven in practice is, in this respect, characterised in that the means of adjustment contains an electronically controlled actuator that is linked to the first knife. The actuator can for example be a spindle that is driven by an electrical stepper motor or an adjustment cylinder that is possibly hydraulic. In both cases, the first knife can be accurately adjusted to the desired depth.
The electronic control mechanism for the second knife can also be implemented in various ways. Another particular embodiment of the device according to the invention is also characterised in that the electronically controlled mechanisms for the second knife contains an electronic clutch that is incorporated in a transmission between a drive for the chassis and a cam disc on which the second knife rests under spring pressure. As soon as the clutch is activated, the cam disc will be driven and the second knife will be released so that the sod is chopped. This can for example be controlled by a central processing unit.